COMMITMENTS AND CONTINGENCIES, Development, Expansion and Renovation Projects and Pending Dispositions (Details)
 3 Months Ended 9 Months Ended
Jan. 31, 2016
USD ($)
ft²
shares
Unit
Jan. 31, 2015
USD ($)
Jan. 31, 2016
USD ($)
ft²
shares
Property
Unit
Jan. 31, 2015
USD ($)
Real Estate Properties [Line Items]        
Anticipated total cost [1] $ 178,190,000   $ 178,190,000  
Project costs incurred to date [1] 156,955,000   156,955,000  
Construction interest capitalized 1,000,000 $ 1,400,000 4,400,000 $ 3,600,000
Deer Ridge - Jamestown, ND [Member]        
Real Estate Properties [Line Items]        
Project costs incurred to date 14,300,000   14,300,000  
Cardinal Point, Grand Forks, ND [Member]        
Real Estate Properties [Line Items]        
Project costs incurred to date 23,000,000   23,000,000  
71 France - Edina MN [Member]        
Real Estate Properties [Line Items]        
Project costs incurred to date 41,300,000   41,300,000  
Other [Member]        
Real Estate Properties [Line Items]        
Project costs incurred to date [1] $ 3,524,000   $ 3,524,000  
Multi-Family Residential [Member] | Deer Ridge - Jamestown, ND [Member]        
Real Estate Properties [Line Items]        
Number of apartment units | Unit 163   163  
Anticipated total cost [1] $ 24,874,000   $ 24,874,000  
Project costs incurred to date [1] $ 24,874,000   $ 24,874,000  
Estimated quarter for completion     4  
Estimated year for completion     2016  
Multi-Family Residential [Member] | Cardinal Point, Grand Forks, ND [Member]        
Real Estate Properties [Line Items]        
Number of apartment units | Unit [2] 251   251  
Anticipated total cost [1],[2] $ 48,242,000   $ 48,242,000  
Project costs incurred to date [1],[2] $ 48,242,000   $ 48,242,000  
Estimated quarter for completion [2]     4  
Estimated year for completion [2]     2016  
Multi-Family Residential [Member] | 71 France - Edina MN [Member]        
Real Estate Properties [Line Items]        
Number of apartment units | Unit [3] 241   241  
Anticipated total cost [1],[3] $ 73,290,000   $ 73,290,000  
Project costs incurred to date [1],[3] $ 69,105,000   $ 69,105,000  
Estimated quarter for completion [3]     1  
Estimated year for completion [3]     2017  
Interest in joint venture 52.60%   52.60%  
Area of real estate property | ft² 21,772   21,772  
Multi-Family Residential [Member] | Monticello Crossings - Monticello, MN [Member]        
Real Estate Properties [Line Items]        
Number of apartment units | Unit 202   202  
Anticipated total cost [1] $ 31,784,000   $ 31,784,000  
Project costs incurred to date [1] $ 11,210,000   $ 11,210,000  
Estimated quarter for completion     2  
Estimated year for completion     2017  
Multi-Family Residential [Member] | Rochester, Minnesota [Member]        
Real Estate Properties [Line Items]        
Number of properties pending acquisition | Property     4  
Number of apartment units pending acquisition | shares 393   393  
Purchase price of pending acquisition     $ 72,500,000  
Cash to be paid for pending acquisition $ 47,500,000   47,500,000  
Value of limited partnership units to be issued in pending acquisition $ 25,000,000   $ 25,000,000  
Multi-Family Residential [Member] | St. Cloud, Minnesota [Member]        
Real Estate Properties [Line Items]        
Number of properties | Property     8  
Sales price of pending disposition     $ 5,600,000  
Unimproved Land [Member] | River Falls, Wisconsin [Member]        
Real Estate Properties [Line Items]        
Sales price of pending disposition     20,000  
Healthcare [Member] | Omaha, Nebraska [Member]        
Real Estate Properties [Line Items]        
Sales price of pending disposition     $ 24,400,000  
[1] Includes costs related to development projects that are placed in service in phases (Deer Ridge - $14.3 million, 71 France - $41.3 million, Cardinal Point - $23.0 million).
[2] Anticipated total cost as of January 31, 2016 includes incremental cost increase due to the replacement of the project's original general contractor. There may be additional costs for this project as it nears completion in the fourth quarter of fiscal year 2016.
[3] The project is being constructed in three phases by a joint venture entity in which we currently have an approximately 52.6% interest. The anticipated total cost amount given in the table above is the total cost to the joint venture entity. The anticipated total cost includes approximately 21,772 square feet of retail space.